The practice of dynamically changing the pitch of the strings on a banjo to create a unique sound, commonly called “slurring”, goes back many years. The first method used was that the musician simply grabbed the string by hand, pulled on it, and used his ears to detenmine how far to pull the string.
A mechanical device that does the same thing became known as a D-Tuner. With a D-Tuner, you can not only slur the strings, you can change the tuning of the banjo form the normal G tuning to D tuning. There are two reasons for changing to D tuning. First, you simply want to play a song in D and second, to use the D-Tuner to temporarily play the D Chord without having to fret the strings while playing a song that is played in the key of G. In the process of changing the tuning, the musician normally slurs the strings going down to produce the tones for the D chord then slurs it going back up to the G chord or G tuning. In some cases the slurring is a quick motion of down and back up immediately. In other cases they vary the speeds to produce unique slurring sounds.
Earl Scruggs was probably the first known banjo player to use a mechanical D-tuner, around 1940. Since that time, there have been untold numbers of all sorts of mechanical devices to perform that function, varying from the crudest of devices to very fancy and very expensive custom made devices. It's unlikely that any of these devices were ever produced commercially. All of these devices were attached to the top side of the banjo's peghead and used some sort of cam device to push and deflect the strings sideways. There were many reasons why these devices never became commercial. The barriers to commercializing included, among others, high production costs, poor performance, poor functionality, inaccuracy, undesirable appearance, and the requirement to drill holes in the sacred cow, the peghead.
The first D-Tuner to go commercial appeared around 1970 and is known generally as the Keith tuner. The Keith tuner addressed most of the disadvantages or problems of all previous tuners. It solved the problem of appearance and the need for drilling holes in the peghead by replacing the existing tuning pegs with a dual purpose tuner that could tune the string in the normal fashion and also perform as a D-Tuner. The Keith tuner did not however solve one important problem of performance. It is very difficult to set the stops properly and they have a definite tendency to slip out of tune. The user is caught between tightening the screws to tight and damage the tuner or tightening it too loose and damage it from slipping during use. The locking screws can also come loose and become lost along with the spring that is suppose to prevent them from coming off. This is evidenced by replacement screws and springs being listed in catalogues. Another disadvantage of the Keith tuner is that you cannot tweak the tuning of the strings without resetting both the up and down stops.
U.S. Pat. No. 7,109,405 to Brown addresses the functionality and reliability issues inherent in prior D-Tuners, as well as issue of holes in the peghead. The Brown patent discloses a D-Tuner having a base unit with a pair of projections extending upwardly from it and a bar for attachment to the base unit with the neck of a stringed instrument clamped between the base unit and the bar. The tuner includes tuning screws for moving the projections linearly to change string tension, a pair of externally threaded posts extending from a bottom surface of the base unit, and nuts to secure the tuner on the stringed instrument.
There is a need for a D-Tuner for a banjo or other stringed instrument, which does not detract from the aesthetic appearance of the banjo, which can be marketed at a reasonable price, which can be easily mounted on a banjo, and which can be used to easily, quickly and accurately tune the banjo.